Removes the `_` prefix from the RSC and Router headers as nginx strips
`_` prefixed headers by default.
Fixes#42164
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## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
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## Feature
- [ ] Implements an existing feature request or RFC. Make sure the
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This masks flight parameters from middleware so it doesn't interfere with RSC or routing.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
Co-authored-by: Tim Neutkens <6324199+timneutkens@users.noreply.github.com>
